docs: def extract_density(population, plane='xy', bins=100, neurite_type=NeuriteType.basal_dendrite):
      '''Extracts the 2d histogram of the center
         coordinates of segments in the selected plane.
      '''
      segment_midpoints = get_feat('segment_midpoints', population, neurite_type=neurite_type)
      horiz = segment_midpoints[:, 'xyz'.index(plane[0])]
      vert = segment_midpoints[:, 'xyz'.index(plane[1])]
      return np.histogram2d(np.array(horiz), np.array(vert), bins=(bins, bins))